Princípios de Comunicação EtherNet/IP

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<p>1</p><p>Industrial Communication Whitepaper</p><p>Principles of</p><p>EtherNet/IP</p><p>Communication</p><p>2</p><p>Contents</p><p>Introduction ......................................................................................................................3</p><p>Producer/Consumer Model ..............................................................................................4</p><p>EtherNet/IP Messaging Types .........................................................................................7</p><p>Real Time Data Exchanges .............................................................................................9</p><p>Typical Network Implementation....................................................................................10</p><p>3</p><p>Introduction</p><p>The Common Industrial Protocol, also known as CIP, is an application layer protocol that provides</p><p>connection between industrial devices across multiple networks. CIP protocol is the common</p><p>application layer across EtherNet/IP, CompoNet, DeviceNet, and ControlNet. CIP gives the user</p><p>the ability to transport control oriented data associated with I/O devices and other information such</p><p>as configuration parameters and diagnostics.</p><p>Figure 1: CIP Protocol Stack</p><p>CIP uses object modeling to describe the structure, operation and functionality of devices. A CIP</p><p>node is described by a collection of objects and device profiles that define common interfaces and</p><p>behaviors. Most objects are common across all supported networks. Objects divide the</p><p>functionality of a device into logically related subsets. These objects interact to provide a basic</p><p>product behavior.</p><p>4</p><p>Identity</p><p>Object</p><p>Application</p><p>Objects</p><p>Assembly</p><p>Object</p><p>UCMM</p><p>Message</p><p>Router</p><p>I/O MsgExplicit Msg</p><p>Connection</p><p>Network</p><p>Link</p><p>Object</p><p>TCP Data</p><p>Encapsulation Data Encapsulation Header</p><p>TCP Header IP Header Ethernet</p><p>Header is 58 bytes</p><p>Figure 2: Object Oriented Data Model</p><p>EtherNet/IP is the implementation of CIP protocol over standard Ethernet. EtherNet/IP defines the</p><p>encapsulation protocol used to structure the CIP data found in the TCP Data field. All</p><p>encapsulated TCP or UDP messages are sent to port 0xAF12. The encapsulation message</p><p>consists of two parts:</p><p> Encapsulation Header</p><p> Encapsulation Data</p><p>Figure 3: EtherNet IP Encapsulation Format</p><p>The encapsulation protocol defines the communications relationship between two nodes as a</p><p>Session. A session is similar to a connection. It sets up the TCP resources, i.e. “opens a socket”.</p><p>Once a session is opened, it remains open until:</p><p> The target or originator closes the TCP resources</p><p> The TCP resources breaks down, i.e. reaching the limit for TCP connections</p><p> Either one of nodes closes the session</p><p>5</p><p>Producer/Target</p><p>Consumer/</p><p>Originator</p><p>Producer/</p><p>Target</p><p>Producer/</p><p>Target</p><p>Producer/Consumer Model</p><p>The EtherNet/IP protocol uses the producer/consumer architecture for I/O data transfer.</p><p> Producers are the field devices that generate data onto the network. Generally, Producers</p><p>generate data at a pre-established rate, without requiring a request to be issued each time.</p><p>Producers are equivalent to Servers in a Modbus environment. This pre-established rate is</p><p>referred to as RPI, Request Packet Interval. The RPI is a configurable parameter and part</p><p>of the module’s configuration.</p><p> Consumers are the devices on the network that make use of the data generated by</p><p>Producer devices. These devices establish the rules for the data to be generated by other</p><p>devices. If necessary the Consumers will write any required output data to the Producers</p><p>at the same RPI rate. Consumers are equivalent to Clients in a Modbus environment.</p><p> Any device may act as a Producer, a Consumer or both, depending on the device’s</p><p>capabilities.</p><p>Figure 4: Producer/Consumer Model</p><p>6</p><p>When talking about I/O Data exchange you may also hear terminology such as originator or target</p><p>devices.</p><p> Originators are devices that initiate any data exchange with other devices on the network.</p><p>This applies to both I/O communications and service messaging. This is the equivalent of</p><p>the role of a Client in a Modbus network.</p><p> Targets are the devices that address any data requests generated by Originators. This</p><p>applies to both I/O communications and service messaging. This is the equivalent of the</p><p>role of a Server in a Modbus network.</p><p>Some Consumer devices are capable of assuming the role of a producer. Schneider Electric’s</p><p>implementation of peer to peer communication makes use of this feature. In order to synchronize</p><p>data from one PLC system to another, the EtherNet/IP module in the PLC rack will assume a role</p><p>of a Target device simultaneously to their role as an Originator.</p><p>Figure 5: Dual Role Producer/Consumer Model</p><p>Producers</p><p>Consumer</p><p>Consumer &</p><p>Producer</p><p>7</p><p>EtherNet/IP Messaging Types</p><p>EtherNet/IP defines two types of messaging types, Implicit, and Explicit Messaging.</p><p>Figure 6: Implicit and Explicit Messaging</p><p>Implicit messaging is used for I/O data exchange. It is based on UDP protocol for faster delivery</p><p>and optimized performance, due to its low overhead and resource consumption. The EtherNet/IP</p><p>communication module on the PLC is the Originator and requests data from the Target devices.</p><p>The Originator dictates the RPI, rate at which it wants to exchange the data with each Target</p><p>device in its configuration; using a specific EtherNet/IP command called Forward Open.</p><p>Once the Target devices acknowledge the connection they will start producing the requested data</p><p>at the rate indicated by the Originator. If required, the Originator will also start writing any data onto</p><p>the Target devices at the same rate.</p><p> Message construction:</p><p>o The initial communication from the Originator to the Target is a Unicast* TCP message.</p><p>o The data produced by the Target devices are Multicast** UDP messages, unless the</p><p>user configures them differently.</p><p>o The “write” commands from the Originator to the Target are Unicast TCP messages.</p><p>* Unicast message is communication between a single sender and a single receiver</p><p>** Multicast message is communication between a single sender and multiple receivers.</p><p>As mentioned Implicit messaging is used when I/O data must be exchanged at a constant rate.</p><p>Such as:</p><p> Scanning various IO modules</p><p> Updating a variable speed drive</p><p> Reading input data on sensors</p><p>Application</p><p>Transport</p><p>Network</p><p>Data Link</p><p>Physical</p><p>HTTP OPC Modbus SNMP</p><p>ARP</p><p>IGMP</p><p>RARP</p><p>IP</p><p>Explicit</p><p>Messaging</p><p>IEEE 802.3 Ethernet</p><p>Implicit</p><p>Messagin</p><p>UDP TCP</p><p>FTP</p><p>OSPF</p><p>CIP</p><p>8</p><p>As an example, a Consumer is requesting data to be provided to it every 20ms. After a successful</p><p>Forward Open message the Producer will publish its data to a multicast address every 20ms. The</p><p>Consumer is a subscriber to that multicast address and it is able to obtain the required information.</p><p>At the same time the Consumer will update the Producer’s output data at the same rate of 20ms</p><p>but using a TCP Unicast message.</p><p>Figure 7: Sample Message Flow</p><p>Explicit messaging is used for exchange of non-cyclic and non-time critical data between</p><p>devices in the EtherNet/IP network. Explicit messages are TCP/IP based messages where the</p><p>EtherNet/IP module sends a request to the Target device and the Target device responds to that</p><p>request. Explicit messages are TCP base messages.</p><p> Message construction:</p><p>o The initial request from the Originator to the Target is a Unicast TCP message.</p><p>o The responses from the Target to the Originator are also Unicast TCP messages</p><p>Explicit messages are typically used to obtain information from the target devices. Some of the</p><p>services include:</p><p> Get_attribute_single</p><p> Reset</p><p> Start</p><p> Stop</p><p>Consumer Producer</p><p>RPI: 20 ms</p><p>Forward Open</p><p>TCP Unicast Msg</p><p>20</p><p>40</p><p>60</p><p>O ->T write output data (TCP)</p><p>T ->O Producing input data (UDP)</p><p>O ->T write output data</p><p>T ->O Producing input data</p><p>O ->T write output data</p><p>T ->O Producing input data</p><p>T</p><p>im</p><p>e</p><p>m</p><p>s</p><p>9</p><p>Real Time Data Exchanges</p><p>The following are the most typical forms of data exchanges found on an EtherNet/IP network.</p><p>Note: T = Target; O = Originator</p><p>a) PLC to I/O Target Device</p><p>Function Packet type Direction</p><p>Comm.</p><p>Type</p><p>Configuration</p><p>i.e. Parameter, RPI</p><p>TCP O  T Unicast</p><p>UDP T O Multicast</p><p>Implicit Messaging</p><p>TCP O  T Unicast</p><p>Explicit Messaging TCP T O Unicast</p><p>b) PLC to PLC</p><p>Function Packet type Direction</p><p>Comm.</p><p>Type</p><p>UDP T O Multicast</p><p>Implicit Messaging</p><p>TCP O  T Unicast</p><p>Explicit Messaging TCP T O Unicast</p><p>C) HMI</p><p>Function Packet type Direction</p><p>Comm.</p><p>Type</p><p>Explicit Messaging TCP T O Unicast</p><p>c) SCADA</p><p>Function Packet type Direction</p><p>Comm.</p><p>Type</p><p>Explicit Messaging TCP T O Unicast</p><p>Configuration Custom protocols or drivers required</p><p>10</p><p>Typical Network Implementation</p><p>The following is an example of a typical EtherNet/IP network.</p><p> PLC: Schneider Electric Quantum</p><p> Network modules: Schneider Electric 140 NOC 771 00 EtherNet/IP network modules</p><p>○ Module Capacity: 7500 packets per second maximum (for Implicit and Explicit</p><p>messaging)</p><p> 60 Target EtherNet/IP Devices being scanned by the network module</p><p> Network transmission rate: 100 Megabits per second (Mb/sec)</p><p>Network parameters</p><p> I/O communications should not exceed 90% of the EtherNet/IP module’s I/O capacity</p><p> On average, each packet contains 58 bytes of I/O module specific data, leading to a</p><p>total packet size of 100 bytes</p><p>Network load</p><p> I/O impact - On average, a typical Ethernet implementation will consume less than 6% of bandwidth to</p><p>support I/O communications.</p><p>Module capacity 7 500 Packets per second</p><p>Allocated capacity 90%</p><p>6 750 Packets per second</p><p>I/O data size 58 Bytes per packet</p><p>Ethernet header* size 42 Bytes per packet</p><p>Total packet size 100 Bytes per packet</p><p>Transmission total 675 000 Bytes per second</p><p>5 400 000 Bits per second</p><p>Line capacity 100 x106 Bits per second</p><p>Line utilization 5.4%</p><p>*Ethernet header includes the following: Ethernet, IP and UDP header</p><p>Load calculation: Load = (number of packets per connection) x (number of connections)/ RPI</p><p>In this case, the maximum load of the module is known and the RPI must be determined: (number</p><p>of packets per connection) x (number of connections) /Load = RPI</p><p>(2 x 60)/6750 = 0.018 seconds or RPI = 18 ms</p><p>The above load impact is on a link with most traffic, which is the connection between the switch</p><p>and the Originator. The traffic on the link to the Target devices will be fraction of that load.</p><p>Approximately, the load on each of the Target’s link will be around 0.09%.</p><p>11</p><p>Total of 60</p><p>Target</p><p>devices</p><p>Figure 8: Example of EtherNet/IP Network</p><p>12</p><p>> Make the most of your energy</p><p>Schneider Electric Industries SAS</p><p>35, rue Joseph Monier Due to possible changes in standards and equipment, the features described in this document</p><p>F-92500 Rueil-Malmaison in the form of text and images are subject to confirmation by Schneider Electric.</p><p>FRANCE Whitepaper by Nazie Champey</p><p>Tél. : +33 (0) 1 41 29 70 00 Design: Schneider Electric</p><p>www.schneider-electric.com</p>